This invention is generally directed to toner compositions and developer materials containing such compositions, as well as the use of these materials in electrostatographic imaging systems, particularly those systems wherein the photoresponsive device has been charged negatively. More specifically, the present invention is directed to developing compositions wherein the toner component is charged positively by certain charge control additives, which toner compositions having improved particle to particle uniformity, fast admix charging, narrow charge distributions, improved humidity stability, improved thermal stability, improved resin dispersibility, and improved carbon black dispersion.
The utilization of charge enhancing additives are known in the prior art, these additives being used primarily for the purpose of imparting a positive charge to the toner composition. There is described for example in U.S. Ser. No. 911,623, filed on June 1, 1978, in the name of C. H. Lu, developing compositions comprised of toner particles, carrier particles and as a charge control additive an alkyl pyridinium halide, such as cetyl pyridinium chloride. Also there is disclosed in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium compounds as charge control agents for electrostatic toner compositions. According to the disclosure of this patent certain specific quaternary ammonium compounds when incorporated into toner compositions were found to provide a toner which exhibited relatively high uniform and stable net toner charge when mixed with a suitable coated carrier coating. U.S. Pat. No. 4,079,014 contains a similar teaching with the exception that a different charge control agent is utilized, namely a diazo type material.
While some of the above developing compositions are suitable for certain purposes, their incompatibility with the toner resin causes difficulties in obtaining uniform dispersions of such materials in the toner formulation comprised of toner resins and carbon black. Further, some of the prior art charge enhancing additives when incorporated into toner compositions migrate to the toner surface at high relative humidity, causing the electrical properties of the resulting developer composition to be adversely affected. Also as it is very difficult to uniformly disperse or dissolve many of the prior art charge enhancing additives, in toner compositions, there results particle to particle non-uniformity, and in some instances an undesirable wide distribution of electrical charge which is not desired.
There continues to be a need for developing compositions which can be used in imaging systems wherein the photoresponsive member is charged negatively, and more specifically, there continues to be a need for improved toner compositions which are positively charged and contain therein charge enhancing additives which are not only soluble in organic materials, but are also humidity insensitive. Additionally there continues to be a need for toner compositions which will rapidly charge new uncharged toner particles being added to a developing composition comprised of charged toner particles and carrier particles, and wherein the charge enhancing additive employed is compatible with the toner resin. Further, there is a need for positively charged toner compositions which do not decompose at high temperatures, thus enabling such compositions to be subjected to a fusing operation.